Expander for polymeric material



May 24, 1966 H. A. EHRENFREUND 3,252,228

EXPANDER FOR POLYMERIC MATERIAL Filed April 23, 1962 5 Sheets-Sheet l w.P N INVENTOR. 3

Her-Aer?! A ffiren/reamd BY (25 47641 manv7$ May 4, 1966 H. A.EHRENFREUND 3,252,228

EXPANDER FOR POLYMERIC MATERIAL 5 Sheets-Sheet 5 Filed April 23, 1962Hererz A fire fray/1d BY 9071M @d'on n S United States Patent O3,252,228 EXPANDER FOR POLYMERIC MATERIAL Herbert A. Ehrenfreund,Longmeadow, Mass., assignor to The Lodge & Shipley Company, Cincinnati,Ohio, a corporation of Ohio Filed Apr. 23, 1962, Ser. No. 191,669 5Claims. (Ci. 34-57) This is a continuation-in-part of my earlierapplication Serial No. 168,408, filed January 24, 1962, now abandoned.

This invention relates to the expansion of thermoplastic particles, andmore particularly to improved means for expanding such particles. Oneimportant aspect of this invention is the preliminary treatment ofmoldable expandable thermoplastic particles prior to molding, anotherpertains to the expansion of thermoplastic particles adapted for variousother uses, such for example as strands used in loose fill packaging.

It is conventional practice in molding foamable or expandablethermoplastic particles or beads such as polystyrene, polyvinyl chlorideand the like, to partially or incompletely expand the beads beforeintroducing them into a mold. Pre-expansion permits molding to becarried out at lower mold pressures and results in a substantiallyfaster molding cycle.

Commercially available expandable polymeric particles contain suitableorganic volatile liquid blowing or raising agents such as pentane,hexane and the like. In conventional processes, polymeric particles arepartially expanded by heating for a predetermined length of time so onlya portion of the blowing agent evaporates. The pro-expansion isconventionally carried out in hot water or steam. After pro-expansion,the beads must be dried for a considerable length of time, on the orderof 24 hours, before they can be properly used in the mold. Failure todry the beads results in irregular expansion during molding, known asthermal shock. Thermal shock is caused by the moisture on the beadswhich mustbe evaporated before the bead temperature can be substantiallyincreased. During molding, as soon as the moisture layer is evaporated,the bead temperature rises too sharply, with the result that many of thebeads are crushed or damaged. 1

While one important advantage of this invention is the dry partialexpansion of moldable particles, whatever the utility of expandedpolymeric material it has been found that the use of moisture inexpanding the particles is undesirable because the material cannot beused immediately for its intended purpose since surface moisture must beremoved. This usually requires a drying time of about 24 hours and callsfor provision of substantial storage facilities.

Conventional mechanical handling of expandable polymeric material tendsto damage or dent the particles, making uniform particle size anddensity diflicult of attainment. Moreover, this particle damage usuallyrequires wasteful additional expansion to achieve the final desired bulkdensity, which substantially reduces the quantity of residual blowingagent for the molding operation.

Another drawback of conventional steam p-re-expansion is the difficultyencountered in providing an eflicient and accurate density controltechnique, since it is necessary to dry a volumetric sample of the beadsbefore weighing for density.

It is the principal object of this invention to provide an improvedapparatus for expanding polymeric material to a selected bulk densitydepending upon the use to which the material is to be put.

It is another object of this invention to provide an improved means ofaccurately controlling the bulk den- 3,252,228 Patented May 24, 1966sity of expandable polymeric beads to a predetermined value suitable forsubsequent molding operation.

It is a further object of this invention to provide a machine forautomatically and continuously controlling the bulk density of polymericbeads.

It is still another object of this invention to provide a means ofexpanding polymeric particles which minimizes particle damage andproduces particles having a high degree of uniformity as to size anddensity.

And another object of this invention is to provide a means of expandingfoamable thermoplastic particles so as to enable immediate use of theparticles without delay for drying.

The above and other objects and advantages of this invention will bemore readily apparent from the following description and with referenceto the accompanying drawings in which:

FIG. 1 is a perspective view of a machine embodying this invention;

FIG. 2 is an elevational view on an enlarged scale of a portion of themachine shown in FIG. 1 and with parts in section;

FIG. 3 is an elevational view on an enlarged scale of a portion of themachine shown in FIG. 1; and

FIG. 4 is a schematic wiring diagram of the electrical control system,for controlling operation of the machine embodying this invention.

The raw materials to be expanded, in accordance with this invention, arein the form of particles or granules which contain a blowing agent andhave a granular den sity on the order of 40 lbs. per cubic foot. Formolding purposes it is generally desirable to reduce the density to therange of l to 3 lbs. per cubic foot. T o accomplish proper particleexpansion, it has been found that the granules must be-heated so thatthey are soft but not sticky. This is possible because there is a shorttemperature range in which the thermoplastic softens without completemelt and coalescence.

It has been determined that the expanding of foamable bulk materials isa true time-temperature relationship and in order to obtain uniform bulkdensity, each of the particles must be removed from the heat source asits density reaches the desired value.

Referring in detail to the drawing, in FIG. 1 is shown anoverall view ofa machine embodying this invention. As shown, themachine comprises ahopper 6 by which thermoplastic particles or beads, such as shown at 8,are supplied by gravity-feed into a pre-heating chamber 10. From thechamber 10 the beads are introduced into an expansion unit, showngenerally at 12, in which the bulk density of the beads is decreased toa predetermined value by entraining the beads in a heated, essentiallydry, air current.

As the beads expand attaining a predetermined density, they aredisentrained or extracted from the air current and deposited in adensity control unit 14. The control unit 14 continuously andautomatically compares the bulk density of the bead output from theexpansion unit 12 with a pre-set valve computing density error. As afunction of the density error, a signal is generated which automaticallyvaries the temperature of the air flowing through the expansion unit, ashereinafter described. In this way it has been found that the density ofthe beads can be continuously and automatically maintained at a selectedvalue, with a high degree of accuracy. A storage chamber, showngenerally at 16, is provided to receive the beads from the control unitand to store them for sub-sequent use in a molding machine.

The hopper 6 may be any suitable construction and as shown is providedwith avalve operable by member 15 for controlling the feed rate of rawbeads from the hopper into the pre-heater 10.

As shown, the pre-heater is in the form of an elongated cylindricalconduit in which is disposed a screw type conveyor 18. The conveyor 18may be driven by any suitable means such as the chain and sprocketarrangement indicated generally at 20, which may be driven by a motor21. From the hopper 26 to the expansion unit 12, the beads are heated byelectrical resistance heaters 19 which surround the cylindrical conduit,generally along its entire length. The heaters are operated atsuflicient temperature to raise the temperature of the beads to a pointjust below the expansion temperature which is about 180 F. forpolystyrene beads marketed by the major suppliers. The screw 18 iscontinuously driven to convey and agitate the beads so as to minimizethe tendency of the beads to agglomerate or fuse together in thecylindrical conduit. For expansion of strand type material pre-heatingmay be dispensed with and the material introduced directly into theexpansion unit 12.

From the conduit, the pre-heated beads are introduced into the expansionunit 12 through an air duct 22, which extends through the wall of. outercasing 24 and communicates with the interior of an air flow unit 26disposed within the outer chamber. The periphery of the unit 26 isspaced from the wall of the outer casing to permit the beads freepassage therebetween. The outer end of the air duct 22 is connected tothe output of a centrifugal fan or impeller 28.

The casing 24 provides means for collecting expanded beads and isprovided with an opening 30; at the bottom through which the beads areemitted and deposited in the control unit 14. An air duct 32 extendsinto the outer casing 24 approximately at the center of the top wall 34.The end of the duct 32 within chamber 24 is provided with a screen 36 toprevent the thermoplastic beads entering the duct and air supply system.An air baffle or deflector .plate 38 is located at the bottom of thescreen 36. The duct 32 extends from the top of the chamber 24 to anelectrical heating unit 40 operated to heat the bead-carrying air to atemperature above 180 F., the expansion temperature of most expandablepolystyrene beads. From the heater 40 an air conduit or duct 42 extendsto the air impeller 28. The air supply system is completed by the duct22 which opens into the inner chamber 26. An air flow loop thusoriginates at the fan 28, through duct 22 into the air flow unit 26which includes an annular chamber 44 and an upwardly opening stack 46.Sufficient velocity is imparted to the air to maintain the beads insuspension in the air and to carry them around the annular chamber 44and up the stack when the density has been sufficiently reduced. Afterrising through the stack the air is deflected outwardly by the platebefore being drawn into the conduit 32. The air flow loop is completedthrough the heater 40 back to the fan 28.

The unit 26 includes the annular or toroidal-shaped chamber 44 which isgenerally circular in cross section. The stack 46 is disposed coaxiallyof the annular chamber 44 and its lower end communicates with the innerradial portion thereof. The stack provides a vent or path for risingheated air coming from horizontal chamber 44. A destaticizing rod 47depends from plate 38 along the axis of the stack and is electricallycharged to neutralize electrical charges carried by the beads. The upperend of the stack 46 terminates in spaced relation below the airdeflector plate 38. The lower inner wall portion of the annular chamberis in the form of a concavely curved, conical member 48. The conicalmember is secured to a hub 50 (FIG. 3) carried on the end of a shaft 52driven by a motor 54 in the direction of the air flow in the annularchamber. Adjacent the lower edge of the rotating conical member are aplurality of circumferentially spaced vanes 56 which serve to impart tothe air flowing in the annular chamber a rotational component which isgenerally perpendicular to the main flow whereby the resultant flowfollows a helical type path 4 around the inner surface of the annularchamber, such as indicated by the arrows in FIG. 3. The air flow unit 26is provided with a conical skirt 58 which flares outwardly anddownwardly from the top of the stack 46 to the periphery of the annularchamber 44. The skirt 58 insures all expanded heads will be deposited inthe control unit 14. A vibrator 59 is provided on the casing 24 tominimize the incidence of beads adhering to the walls of the system.

The annular chamber 44 serves to provide an endless horizontal path inwhich the polymeric beads may be entrained in a heated, essentially drycurrent of air, and with the beads discretely held in suspension. Theair current generated by the fan 28 moves in an annular path about avertical axis. The vanes 56 impart to the air current a rotation oragitation such as indicated by the arrows in FIG. 3. The beads deriveheat for expansion for the air in which they are suspended in spacedrelation whereby there is little incidence of bead damage as in a batchprocess. When the airentrained beads have reached a predetermineddensity, they will be carried by the rising air current which passesupwardly in the stack 46. The beads are air suspended in the rising hotair current in the stack 46 until their density reaches a pre-set value.As the density of each plastic bead decreases to the pre-set value, itwill be carried out of the stack and extracted or disentrained from theair flow. Extraction of the expanded beads is accomplished by deflectionof the air current outwardly of the stack 46 suflrcient to enablegravity to overcome the carrying capacity of the air flow. Thus theheads will fall downwardly about the outer surface of the air flow unit26 and be deposited in the control unit 14.

The density control unit 14 comprises a conveyor in the form of anendless belt 60 disposed around a pair of spaced rolls 62 and 64. Asshown, the roll 62 is driven by motor 63 so-that the upper span of theconveyor belt moves toward roll 64 traversing a weighing scale forcontinuously and automatically weighing a given volume of bead productreceived from the expansion unit.

The weighing unit may be any suitable type such as 2. Builders IronFoundry (B.I.F.) scale which, as shown in FIG. 2, comprises a table 65having two portions 66 and 68 supported in cantilever fashion at theiropposite ends by flexible, spring metal hinge members 70 and 72respectively. The springs are supported by means of blocks 71 aflixed tothe underside of an I-beam 73. The I-beam is mounted on the housing ofthe control unit 14. A vertically adjustable doctor bar 74 is providedfor leveling and controlling the height of beads to be carried by theconveyor belt 60 over the upper surface of the table 65. Thus, for agiven setting of the doctor bar relative to the upper surface of theconveyor belt, a predetermined volume of beads will be weighed. Anydeviation from a pre-set weight, will be indicative of a densityvariation and result in movement of the table portions 66 and 68.

Movement of the table is transmitted to a balance scale beam 75 by alink78, the upper end of which is connected to the beam, the other endof which is connected to a bar member 80. A slidable weight 81 isprovided on the beam 76 on the opposite side of the beam fulcrum 83. Inoperation of the unit, the weight 81 is positioned a set point, apredetermined distance from the fulcrum in accordance with apredetermined scale so that any deviation of the given density willcause the beam 76 to tilt about its fulcrum 83. When the density of thebeads is in conformity with the set point, beam 76 will be balanced.

The bar and another similar bar 82 are spaced below and adjacent theouter side edges of the weighing table. 'The bars 80 and 82 areinterconnected by a cross bar 84 and are supported for verticalpivotable movement intermediate the cross bar 84 and the link 78, byhooks 85. With the arrangement described above and as viewed in FIG. 2,downward table movement about the hinge members 70 and 72 is translatedby linkage 86 into clockwise rotation of the rod 84, while, of course,upward movement results in counterclockwise rotation of shaft 84. Sincethe rod 84 is affixed to the bars 80 and 82, the bars are tilted abouttheir pivot points whereby the link 78 is displaced vertically eitherupwardly or downwardly, depending on whether the bulk density of thebeads is greater or smaller than a pre-set value. For example, when thedensity of the bead product is too large, the table would move downcausing clockwise rotation of rod 84 and consequent clockwise tilting ofbars 89 and 82. This, of course, displaces link 78 downward tilting thebeam 76 clockwise about its fulcrum 83. Too low bead density wouldresult in opposite rotation of beam 76.

On one end of the beam 76 is an electrical coil 90 in which is disposeda ferromagnetic core 92 carried on the outer end of the beam. The coilis electrically tuned with its core in a predetermined position, whenthe beam 76 is balanced. Movement of the beam will move the core 92relative to the turns of the coil causing an electrical signal which, aswill be hereinafter described, causes a change in the temperature of theair current in the expansion unit. The opposite end of the beam 76 isprovided with a dash pot 94 to smooth the movement and damp oscillationsof the beam.

The conveyor belt comprises an endless band of a strong light-weightmaterial such as Mylar. Along its edge the band is provided with aseries of openings 96 (FIG. 1) located and spaced to receive projections98 extending radially from the rolls 62 and 64. It will be noted thatthe roll 62 is the driving roll for the conveyor belt so that the upperspan of the conveyor is pushed rather than pulled over the upper surfaceof the weighing table. It has been found that this arrangement resultsina greater degree of accuracy. From the discharge end of the conveyor thebeads fall into the storage unit 16. A destaticizing rod 99 may belocated adjacent the discharge end of the conveyor to remove any staticcharge carried by the beads before they are deposited into the storageunit.

The storage unit 16 is provided with a beater or agitator 100 to preventthe beads fusing together. As shown, the agitator shaft 101 isrotated bya motor 102. Since the beads are dry they can be used immediately formolding.

In FIG. 4 is shown a wiring diagram of an electrical system foroperating and controlling the operation of the pie-expander. As shown,the entire electrical system is powered by 3-phase, 230-volt electricalpower connected to a switch and fuse unit 110. From the unit 110 leads112, 114 and 116 are connected to motor 54 which rotates the cone 48(FIG. 3). Leads 114 and 116 are also connected to the primary of astep-down transformer 118 which reduces the power to 115 volts, 15amperes.

Leads 112 and 114 are connected to a saturable reactor 120 of the typemanufactured by the West Instrument Co. The air heater 40 is controlledby the reactor 120. Leads 112 and 116 are connected to another saturablereactor 122, similar to the reactor 120; which serves to control thepre-heaters 19. As is well known, a saturable reactor is a magneticamplifier having DC. and A.C. windings disposed on a magnetic core. Theload is in circuit with the A.C. winding, and the DC. winding serves asa control winding. When a DC. signal is received, the voltage across theload increases as a result of the decrease in inductance which is equalto the slope of the hysteresis loop. There is thus an amplifier actionwhereby a small DC. signal results in increased voltage to the othercomponents of the system.

The transformer 118 provides, by means of leads 124 and 126, a powersupply for the other components of the electrical system. A cabinet fan128 and its indicator light 129 are connected across the lines 124 and126 by lead 130 which includes switch 132. A cabinet heater positionsuch as shown in FIG. 1 for maintaining constant atmospheric conditionswithin the cabinet of the control unit. A lamp 144 preferably green, isprovided to indicate that the heater is in operation and the lamp 146,preferably red, is provided to indicate the off condition of the cabinetheater. An overheat relay 147 is operated by a normally closedthermostatically controlled switch 148. If the temperature in thecabinet should exceed a predetermined value, relay 147 will beautomatically operated to open the circuit to the cabinet heater.

A master switch 150 is electrically connected to the lead 124 by meansof a switch 15-2 and a switch 154. The other side of the master switchis connected by a lead 156 to the electronic controller 160, such asmarketed by the West Instrument Co. and which is provided to control theoperation of the heater 40. A switch 162 is provided in line 156 toactuate the heater 40. The controller of the type marketed by WestInstrument Corporation includes a manually operated pointer arm whichmaybe positioned at any desired temperature set point, and a voltmeterpointer or arm movable in response to a signal generated by the coil asa result of movement of core 92 carried on the end of scale beam 76. Thecontroller also includes a small lightsouree and photocell disposed sothat the light is directed onto the cell. An opaque flag or disc iscarried on the voltmeter pointed and disposed to block any light beamstriking the photocell when the pointer is in alignment which the setpoint arm. As long as the light strikes the photocell sufiicient currentis generated in the photocell to actuate the driver chassis 166 whichincludes a magnetic amplifier for supplying electrical power tosaturable reactor wired in series with heater 40. The reactor 120 willvary the power supplied to the heater in response to the output signalof the controller 160 as when the opaque flag carried on the arm of thevoltmeter, interrupts the light beam path to the photocell. When thepre-expanded beads reach a predetermined density a signal is generatedin coil 90, and the movable pointer of the controller would come intoregistration with the set point arm whereby the power supplied to heater40 is reduced.

As herein disclosed, the pre-heaters 19 are controlled in the samemanner as the heater 40 with the exception that a thermocouple isemployed instead of coil 90. The thermocouple 180, disposed in conduit10, generates a minute electrical current, which varies in proportion tothe temperature of the thermocouple. This current causes deflection ofthe voltmeter pointer of controller 163, and the output signal of thecontroller is connected to drive chassis 184 which may be identical tochassis 166. Thus the saturable reactor 122 wired in series with heaters19 will vary the power supplied to the heaters in relation to the lightbeing blocked from a photocell by the pointer flag in the electroniccontroller 163. Lead 158 also extends from the switch and is connectedto another electronic controller 163 similar to the controller 160. Thecontroller 163 is provided for controlling the operation of thepre-heaters 119 (FIG. 1). A

, switch 164 is provided in line 158 to actuate the prethrough a relay170 operated by a thermostatically controlled switch 172 which operatesto cut ofi" the heater 40 if the temperature of the air coming from theheater 40 exceeds a pre-set value. A green indicator lamp 171 isprovided to show the operator whether or not'the controller 160 isenergized. A red indicator lamp 174 is provided to indicate when theunit 166 is de-energized. The unit 166 is electrically connected to thesaturable reactor 120 which, as mentioned above, controls the operationof the heater 40 in accordance with a signal generated by the coil 90.

As shown, the coil 90 is connected to a Taylor Recorder 176 from which asignal is transmitted to the controller 160. In accordance with thesignal developed in the coil, the temperature of the heater 40 isproportionally adjusted to bring the beads to the pre-set density.Moreover, as the density approaches the pre-set value, the heater 28 iscontinuously and automatically adjusted so that the density will notvary or hunt about the pre-set value.

The pre-heaters 19 are controlled by the electronic control unit 163, ashereinbefore described, which is responsive to a signal fromthermocouple 180 located on the conduit 10 (FIG. 1). A cable 182electrically interconnects the controller 163 to a driver chassis 184which, in turn, supplies an electrical signal to the saturable reactor122 connected as previously described to the pre-heaters 19. With thisarrangement, a heat balance is maintained, since the temperature of thepreheaters is adjusted in proportion to the temperature deviation from apre-set value detected by the thermocouple 180. Y The fan 28 is drivenby a motor 186, controlled by a relay 188 in series with the switch 152.The relay circuit 188 is electrically interconnected to the drivechassis 184 by means of a lead 189. An indicator lamp 190 is providedacross the relay as shown when the fan 28 is energized.

The pre-heat motor 21 which drives the conveyor screw 18 is controlledby the switch 154. An indicator lamp 191 provides visual indication ofthe operating condition of the pre-heat motor. A cut-out 122, operatedby a photocell, is provided in the circuit of the pre-heat motor 21 tode-energize the motor if the level of the beads on the conveyor 60exceeds the pre-set height of the doctor bar 74. Switch 124 controls theoperation of the motor 63 which drives the conveyor belt 60. A cut-out196 operated by a photocell is provided in series with the conveyor beltmotor 63 for stopping the conveyor belt whenever the level of the beadsbeing carried on the belt is below the pre-set height of the doctor bar.The cutout 196 is also electrically connected similarly to de-energizethe pre-heater motor 21. Another cutout 198, photo- 1 cell operated,serves to cut oif the pre-heater motor 21 whenever the height of thebeads in the storage tank 16 exceeds a predetermined level.

A switch 200 is connected to a step-up transformer 202 which increasesthe voltage from 115 to approximately 24,000 volts. This high voltage iselectrically connected across static bars 47 and 99 which, as describedabove, serve to neutralize any electrical charge carried by the plasticparticles.

Means is provided to monitor the temperature within the expansion unit12. As shown, this is accomplished by means of thermocouple 203 of thetype marketed by the West Instrument Co.

The interior of the control unit may be provided with suitableillumination. As shown, a cabinet lamp 204 is disposed within the unitand its operation is indicated by a lamp 206 which may be green in colorand controlled by switch 207.

The motor 192 which drives the stirrer in the storage tank may beoperated by an on-01f switch 208. Energization of the motor may beindicated by a green lamp 210. The vibrator 59 and its indicator lamp212 are 'operated by means of a switch 214.

In summary of the operation, polymeric beads are fed from the hopper 26into the pre-heat chamber 10 where they are heated uniformly to atemperature somewhat below that of the actual softening point of theplastic. The material is then introduced into a high velocity aircurrent and carried into the air flow unit 26. The air is essentiallydry and heated above the softening point of the polymeric material. Inthe annular chamber 44 the particles are pneumatically agitated andcirculated, deriving heat from the air in which they are entrained. Theparticles remain in the annular chamber until their bulk density isreduced to about 3 to 4 lbs. per cubic foot. At this density theparticles are individually carried upwardly from the horizontal annularchamber 44 into the upright vent or stack 46. In the stack, theparticles are suspended on the rising column of heated air. Theparticles remain in the stack until the desired volume-to-mass weightratio is achieved, at which point they are carried out of the stack intothe outer casing 24 which is at a lower temperature than the air stream.The path of air flow is deflected by plate 38 and the particles freelyfall into the control unit 14.

The control unit 14 senses the bulk volume of the entire output of thesystem and generates a signal which regulates the temperature of the airheater. Since the velocity of air rising in the stack 46 is a functionof its temperature if the weight of a known volume of material is lowerthan the desired value, the control system increases the amount of heatbeing supplied by the heater 40. This raises the velocity of air risingin the stack and material of higher density will be carried out of thesystem. If the weight of the known volume of material is greater thanthe desired value, the air temperature will be reduced and its velocitycorrespondingly decreased, thus lower density material will be carriedfrom the system.

It has been found that the density control system is capable ofcontrolling the density of the particles within extremely closetolerances. Moreover, the material can be molded immediately withoutdelay for drying, thus facilitating handling and storage.

While the above description has in large measure been concerned with theexpansion of polymeric beads, this invention also relates to thecomplete expansion of polymeric particles regardless of theirconfiguration and utility. Thus, for example, it has been found that thedry expansion of polystyrene strands which may be used as loosepackaging fill has advantages of convenience, simplicity and speed.Moreover, installation of apparatus for carrying out the dry expansionprocess requires no plumbing and drain connections. For such utility, itwill be realized that the degree of accuracy of density controldesirable for bead pre-expansion is not necessary for the completeexpansion of polystyrene strands.

Having thus described this invention, what is claimed is:

1. Apparatus for partially expanding foamable thermoplastic particles toa predetermined bulk density comprismg means for continuously conveyingsaid particles along a predetermined path, means extending over aportion of said path for supporting said particles in a stream of heatedair to expand said particles, the expansion of said particles beingresponsive to a time-temperature relationship, means for measuring thebulk density of the expanded particles as they are moved along saidpath, and

means responsive to said bulk density measuring means for controllingthe velocity of said air stream to achieve said predetermined bulkdensity.

2. Apparatus for expanding foarnable thermoplastic particles to apredetermined bulk density comprising an air chamber open at its upperend, means for impelling air into the chamber at its lower end, meansfor providing a heated upward air current in said chamber having avelocity sufiicient to support said thermoplastic particles in air bornesuspension, said air being heated above the expansion temperature ofsaid thermoplastic particles to supply heat of expansion to saidparticles, means for separating particles from the air current whenexpanded to said predetermined density, means for determining thedensity of the particles so separated from the air current, and meansresponsive to the density determining means for controlling the upwardair current velocity in the chamber to automatically maintain theparticle output of said apparatus at said predetermined bulk density.

3. Apparatus as set forth in claim 2 in which the means for controllingthe velocity of the air current includes means for controlling thetemperature of said air to maintain the expanding particles at saidpredetermined density.

4. Apparatus for expanding foamable plastic particles comprising anannular chamber disposed about a generally upright axis, an uprightstack coaxial with said annular chamber and communicating with the innerradial portion thereof, a casing disposed around said chamber and stackhaving its innner surface radially spaced outwardly thereof, means forsupplying a heated current of air into said annular chamber, a conduitopening through said casing opposite the upper end of said stack, saidconduit communicating with said air supply means, means for introducingthermoplastic particles into said air stream, said air stream havingsufi'icient velocity to carry and maintain said particles in airsuspension, said air being heated to a temperature above the expansionpoint of said particles, said velocity and temperature being sufi'icientto carry particles expanded to said predetermined density out of saidstack, means for laterally deflecting the air flow emanating from saidstack sufiiciently to extract the particles therefrom, said casinghaving a bottom opening for discharging the expanded particles, and aconveyor- 10 scale for continuously determining the density of theexpanded particles.

5. Apparatus as set forth in claim 4 including means for automaticallyand continuously adjusting the velocity of the air in said annularchamber and stack proportional to deviation of particle densitydetermined by said conveyor-sca1e relative to said predetermineddensity.

References Cited by the Examiner UNITED STATES PATENTS 748,893 1/1904Trump 34-57 1,475,502 11/1923 Manning 34-10 1,550,992 8/1925 Trump 34-101,635,527 7/ 1927 Barthelmess.

1,777,670 10/1930 Hausman.

2,054,441 9/ 1936 Peebles 159-4 2,561,394 7/1951 Marshall 159-4 X2,561,395 7/1951 Marshall 159-4 2,571,143 10/1951 Leslie 34-182 2,636,284 4/1953 Napier 34-182 2,664,286 12/ 1953 Frazel 177-16 2,950,261 8/1960 Buchhotz et al 260-25 2,983,692 5/1961 DAlelio 260-25 WILLIAM F.ODEA, Primary Examiner.

LEON I. BERCOVITZ, PERCY L. PATRICK, JOHN J.

CAMBY, Examiners.

M. FOELAK, J. SOFER, Assistant Examiners.

1. APPARATUS FOR PARTIALLY EXPANDING FOAMABLE THERMOPLASTIC PARTICLES TO A PREDETERMINED BULK DENSITY COMPRISING MEANS FOR CONTINUOUSLY CONVEYING SAID PARTICLES ALONG A PREDETERMINED PATH, MEANS EXTENDING OVER A PORTION OF SAID PATH FOR SUPPORTING SAID PARTICLES IN A STREAM OF HEATED AIR TO EXPAND SAID PARTICLES, THE EXPANSION OF SAID PARTICLES BEING RESPONSIVE TO A TIME-TEMPERATURE RELATIONSHIP, MEANS FOR MEASURING THE BULK DENSITY OF THE EXPANDED PARTICLES AS THEY ARE MOVED ALONG SAID PATH, AND MEANS RESPONSIVE TO SAID BULK DENSITY MEASURING MEANS FOR CONTROLLING THE VELOCITY OF SAID AIR STREAM TO ACHIEVE SAID PREDETERMINED BULK DENSITY. 